Many people use mobile stations, such as cell phones, personal digital assistants (PDAs), tablet computers, laptop computers, desktop computers, in-car computers, and so on, to communicate with cellular wireless networks. These WCDs and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Mobile stations typically conduct these wireless communications with one or more base transceiver stations (BTSs), each of which send communications to and receive communications from mobile stations over the air interface. Each BTS is in turn communicatively connected with an entity known as a base station controller (BSC), which (a) controls one or more BTSs and (b) acts as a conduit between the BTS(s) and one or more switches or gateways, such as a mobile switching center (MSC) and/or packet data serving node (PDSN), which may in turn interface with one or more signaling and/or transport networks.
As such, mobile stations can typically communicate with one or more endpoints over the one or more signaling and/or transport networks from inside one or more coverage areas (such as cells and/or sectors) of one or more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typical arrangements, MSCs interface with the public switched telephone network (PSTN), while PDSNs interface with one or more core packet-data networks and/or the Internet.
To meet increasing demand for high-speed data on mobile devices, cellular service providers have begun implementing “4G” networks, which provide service under one or more 4G air interface protocols, such a long-term evolution (LTE) protocol. LTE was developed by the 3rd Generation Partnership Project (3GPP), and is based on GSM/EDGE and UMTS/HSPA network technology.
In the context of LTE, a mobile station is typically referred to as a “user entity” (UE), and may take various mobile and stationary forms, such as a mobile phone, tablet computer, laptop computer, desktop computer, or any other device configured for wireless communication. Herein, the terms “mobile station,” “wireless communication device” (or WCD), and “user entity” (or UE) may be used interchangeably.
Optimally, a wireless service provider will strategically implement base stations throughout a market area so that served WCDs can move between the base station coverage areas without loss of coverage. Each base station may include an antenna structure and associated equipment, and the wireless service provider may connect the base station by a landline cable (e.g., a T1 line) with the service provider's network infrastructure to enable the base station to communicate with a signaling controller (e.g., MME), gateway system, other base stations, and the like.
In practice, however, it may be impractical for a wireless service provider to run landline connections to base stations in certain locations. For instance, where a service provider seeks to provide many small coverage areas blanketing a market area or to fill in coverage holes between coverage of other base stations, the service provider may implement many small-cell base stations throughout the market area, but it may be inefficient or undesirable to run landline cables to every one of those small-cell base stations.
To connect a base station with the network infrastructure in such a situation, the wireless service provider may implement a wireless backhaul connection between the base station and another base station of the service provider's network. In this situation, the base station at issue operates as a relay base station, and the other base station operates as a donor base station. Note that a relay base station may also be referred to as a “mini-macro” (MM) base station.
In practice, the relay base station includes or is coupled (e.g., via a local area network or other connection) with a WCD, referred to as a relay WCD, and the donor base station then serves the relay WCD in much the same way that the donor base station serves other WCDs. Further, the relay base station itself serves WCDs, in much the same way that any base station would.
With this arrangement, when the relay WCD attaches with the donor base station, the relay WCD may acquire connectivity and an IP address as discussed above for instance. But based on a profile record for the relay WCD, the network (e.g., a signaling controller) may recognize that the relay WCD is a relay WCD (rather than a normal end-user WCD) and may therefore set up a bearer connection for that relay WCD with a special core network gateway system (e.g., “SAE GW”) that provides for internal core network connectivity and assigns the relay WCD with an IP address for use to communicate within the core network. Once the relay WCD receives that core network IP address assignment, the relay WCD may then convey that IP address to the relay base station for use by the relay base station as the relay base station's IP address on the core network. The relay base station may then operate as a full-fledged base station of the network, having IP-based interfaces with other core network entities (e.g., a signaling controller, a gateway system, and other base stations), albeit with those interfaces passing via the wireless backhaul connection provided by the relay WCD, and via the core network gateway system.
Once the relay base station is thus in operation, the relay base station may then serve WCDs in the same way as a standard base station serves WCDs. Thus, when a WCD enters into coverage of the relay base station, the WCD may signal to the relay base station to initiate an attach process, the WCD may acquire an IP address, and an MME may engage in signaling to establish one or more bearers between the WCD and a gateway system. Each of these bearers, though, like the relay base station's signaling communication, would pass via the relay's wireless backhaul connection.
In a further aspect of some protocols, such as LTE, reception at cell edges may be problematic for various reasons. For example, the greater distance to a base station at a cell edge may result in lower signal strength. Further, at a cell edge, interference levels from neighboring cells are likely to be higher, as the wireless communication device is generally closer to neighboring cells when at a cell edge.
In an effort to improve the quality of service at cell edges, 3GPP LTE-A Release 11 introduced a number of Coordinated Multipoint (CoMP) schemes. By implementing such CoMP schemes, a group or cluster of base stations may improve service at cell edges by coordinating transmission and/or reception in an effort to avoid inter-cell interference, and in some cases, to convert inter-cell interference into a usable signal that actually improves the quality of service that is provided.
LTE-A Release 11 defined a number of different CoMP schemes or modes for both the uplink (UL) and the downlink (DL). For the downlink, two basic types of CoMP modes are set forth: joint processing (JP) schemes and coordinated scheduling/beamforming (CSCH or DL-CSCH) schemes. For the uplink, numerous types of CoMP modes have been devised.
Uplink CoMP modes may involve interference rejection combining (IRC) or coordinated scheduling for purposes of reducing or preventing interference between transmissions from different user entities (UEs). Additionally or alternatively, various uplink CoMP modes may involve “joint reception” and/or “joint processing.” Joint reception generally involves multiple base stations receiving an uplink signal that is transmitted by a given UE. Joint processing generally involves the multiple base stations that received the uplink signal from the UE, sending the respectively received signals or a decoded and/or processed version of the respectively received signals to one another, or just to a master base station in the group, such that the multiple received versions of the UE's transmission can be combined to improve reception and/or reduce interference.
Various types of joint processing have been implemented on the uplink. For example, joint processing on the uplink can be centralized. When a centralized CoMP mode is implemented on the uplink, the coordinating base stations may simply pass the entire received signal from a given UE on to a master base station, which then uses the received signals from multiple base stations to decode and/or process the signal from the given UE. Joint processing on the uplink can also be de-centralized to varying degrees. Specifically, when a decentralized CoMP mode is implemented on the uplink, a coordinating base station may decode and/or process the received signal from a given UE, and then send the decoded and/or processed signal from the given UE to the master base station. The master base station can then combine or select from the decoded and/or processed versions of the UE's transmission, which are sent to the master base station from one or more coordinating base stations that receive the UE's signal (and possibly a version of the UE's signal that is received at the master base station itself).